Marine Interpretation Message
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
AGPN40 KWNM 211517
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
817 AM PDT Thu Sep 21 2017

.FORECAST DISCUSSION...Major features/winds/seas/significant
.weather for the North Pacific N of 30N and E of 150W.

E Pacific cold front shows up quite well even on IR imagery, and
is currently pushing south across the southern CA offshore
waters this morning. Perhaps even more aesthetically striking,
the boundary is remarkably visible using CIRA layered
precipitable water product. Winds in the vicinity of the
boundary remain weak, generally 20 kt or less, but will be on the
increase quickly today and this afternoon as high pressure
filters SE behind the front; expect bl winds to increase to near
30 kt by 00z, with core of highest conditions near the Channel
Islands. Farther north, weak surface low has developed SW of
Vancouver Island, with winds generally 20 to 30 kt along the west
quadrant of the low. Winds should continue to slowly abate today
as the low moves south and dissipates near Cape Blanco.

Overall the ongoing grids remain in excellent shape this morning,
and can find no reason to make any adjustments based on current
conditions and 06z guidance. Will await the 12z model suite and
re-evaluate forecast accordingly later this afternoon.

-----------------------------------------------------------------
PREVIOUS DISCUSSION...

GOES Water-vapor satellite imagery and lightning data show a
fairly strong upper level trough over the far eastern north
Pacific Ocean early this morning. The trough is moving east and
will likely move inland toward the Rockies later today and
tonight. As the trough moves east, the threat for showers and
thunderstorms will diminished from west to east over mainly
Oregon and northern California offshore waters today into
tonight. Locally gusty winds and rough seas can occur in or near
any of the thunderstorms that occur over the waters. We will
manually add in the shower and thunderstorm chances to the grids
as the available models once again do not appear to be performing
very well regarding the current shower and thunderstorm activity
detected over the region.

Overall, the 00Z models are remaining quite consistent from past
model cycles, and for the most part these models remain in very
good agreement over the region through the weekend into early
next week. For the early morning package, we see no need to alter
the previous grids and forecast too much so we will stay close
to the previous forecast for the early morning package right
through the forecast period, and then populate with the 00Z GFS
10 meter winds to finish up the forecast for days 5-7. We will
make a few manual adjustments to the ongoing grids so that the
early morning OPC forecast fits well with nearby coastal WFO and
TAFB grids. Otherwise, the chance of gales over the offshore
waters will likely remain quite low through the forecast period.
The best chance for gales will occur over the coastal waters near
the northern California and far southern Oregon coasts Sun night
into Mon night as the pressure gradient between high pressure
west of the offshore waters and a coastal trough strengthens. A
cold front will approach the far northwest portion of PZ5 waters
Mon night as low pressure forms along the front to the west and
northwest of the region. Confidence levels are near to above
average over the waters for the next 5 days.

Seas: The latest observations and altimeter data indicates that
the 00Z Wavewatch III and ECMWF WAM models have both initialized
within a foot or two of the data over the region early this
morning. The output from these two wave models appears to be
fairly similar over the offshore waters for the next few days.
We will use a 50/50 blend of the Wavewatch and WAM models for
the early morning package, and continue to manually edit the
wave grid over areas adjacent to the WFO coastal waters and TAFB
forecast areas.

Extratropical Storm Surge Guidance: n/a.


.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
     None.

.PZ6 California Waters...
     None.

$$

.Forecaster Collins/Mills. Ocean Prediction Center.


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.